Unification of Scotland

The Unification of Scotland was the process by which the Pictish kings of Circenn united the Celts of Scotland under a single kingdom, the Kingdom of Scotland, following centuries of warfare and conquest. Kenneth mac Alpin added the crown of Pictland to his domain of Dal Riata in 842, creating the Kingdom of Scotland, and his descendants would go on to conquer the other Gaelic kingdoms of Scotland, fight back Anglo-Saxon encroachment, and defend the realm from Norse Viking invaders and raiders.

Background
In the centurires following the Anglo-Saxon invasions of England, new kingdoms emerged in Wales and Scotland. In Scotland, the emergence of rival kingdoms of the Picts, the Dal Riatan Scots from Ireland, the Strathclyde Britons (whose stronghold was at Dumbarton Castle), and an area ruled from northumbria led to a struggle for power.

History
By the late 6th century AD, the Dal Riata kingdom in southwestern Scotland, which was established by immigrants from northern Ireland over the preceding century, was beginning to make inroads into the lands of the previously dominant Picts.

King Aedan mac Gabrain of Dal Riata, who came to the throne in 576, launched far-flung campaigns in Orkney, the Isle of Man, and central Scotland as far as Stirling. These campaigns, as well as Aedan's possession of ancient Dal Riatan lands in Ireland, created a precocious empire that straddled the Irish Sea.

The defeat and death of Aedan's grandson, Domnall Brecc, at Mag Rath in County Down in 639 led to the total eclipse of the Dal Riatan position in Ireland, and an opportunity for the Pictish kings to reassert themselves in Scotland. However, the growing power of the English kingdom of Northumbria, beginning in the reign of King Oswy (642-70), prevented this. In fact, Oswy may have exacted tribute from the Picts.

In 671, the Picts seem to have revolted against Northumbrian hegemony and as a result, their king, Drest, was expelled. His replacement, Bridei mac Beli, came and exacted Pictish revenge at the Battle of Nechtansmere in 685. In this battle, King Ecgfrith of Northumbria perished along with the prospects of an Anglo-Saxon dominance of southern Scotland.

Disunity among Picts
The Picts themselves were divided into various clan groups and kingdoms. The ruler of one of these in the south, Oengus mac Fergus (Onuist in Pictish), defeated a rival, Elphin, at Moncreiffe near Perth in 728 and conquered northern Pictland and parts of Dal Riata by the late 730s.

A defeat inflicted by the Strathclyde Britons in 740 briefly threatened Onuist's dominance, but in 746 they submitted to him in a treaty at Clyde Rock. Instability in Pictland after the death of Onuist in 751, together with the destabilizing effect of the Viking raids that began in 795 with the attack on Iona, made the Dal Riatans of the southwest much better placed to assume the mantle of Scottish unity in the 9th century.

Getting Scotland together
In 839, the Vikings won a great victory in which Uuen, ruler of the Pictish kingdom of Fortriu, was slain along with Aed mac Boanta, the King of Dal Riata, and "others almost beyond counting." As the grip of the descendants of Onuist over Pictland collapsed, the way was open to new men. One such, Cinaed mac Alpin, or Kenneth mac Alpin, succeeded in adding the crown of Pictland to his existing domain of Dal Riata in 842, thereby uniting the two rival kingdoms for the first time.

Kenneth is conventionally regarded as the unifier of Scotland, but it was by no means certain that his achievement would be any more lasting than those of Aedan or Onuist, and a separate Pictish identity persisted for at least 50 years. Kenneth's brother Domnall mac Ailpin (858-62) and nephew Constantine I (862-76) were both still referred to as "King of the Picts" in the annals.

Constantine had to face a worsening threat from the Vikings as Amlaib, King of Dublin, embarked on a three-year campaign of plunder. This concluded with the capture of Dumbarton, the main stronghold of the Strathclyde Britons in 870. Constantine died in 877 in a battle against the Vikings and for a decade, the Mac Alpin family was excluded from power.

When Constantine's son Domnall regained the throne in 889, it was not as the ruler of the Picts and Scots (Dal Riatans) but as the King of Alba. The long-term survival and unity of this new kingdom of Alba was secured by Domnall's successor, his cousin Constantine II. Over his 40-year reign, Constantine saw the demotion of the former Pictish client kings of Athol, Angus, and Mar to the status of royal stewards (or mormaer) and an increasing confidence in external diplomatic affairs.

Constantine's achievements
It was Constantine II (900-943) who built an alliance of Viking, Strathclyde Britons, and Scots to stem the tide of advance of Aethelstan of Wessex in northern England. The fact that the defeat of the alliance at Brunanburh in 937 did not lead to the collapse of Alba is a testament to Constantine II's achievement in securing its permanence.

Aftermath
Scotland was ruled by the descendants of Kenneth mac Alpin until the reign of Malcolm II (1005-34). At times, they were strong enough to intervene in England. Malcolm II invaded the country while it was weakened by the Viking invasions, and won a victory at Carham on the River Tweed in 1018. Malcolm's grandson Duncan I was deposed by Macbeth, the mormaer of Moray in 1040. From the 1060s, Duncan's restored descendants faced a greater threat from Norman England, which culminated in a series of bitter wars in the 13th century.